Altered proteolytic activity has been associated with cataractogenesis. Cataractogenesis is most frequently associated with aging, and senile cataracts are frequently found in the oldest part or core of the lens. The lens contains significant quantities of Leucine Aminopeptidase (LAP). This research seeks to determine if LAP is damaged with age and/or at the site of cataract by using immunofluorescent localization of LAP in normal and cataractous lens sections. Histochemical activity measurements are also being devised so that the distinction between inactive and active enzyme can be made. Kinetic tests seek to determine the specificity of LAP, with emphasis on gaining information regarding interaction of LAP and physiological substrates. Currently, only model compounds are being assayed. LAP is the only representative of the aminopeptidases which has been crystallized. Elaboration of a mechanism of action for LAP would complete, on a molecular level, an understanding of biological proteolysis since this has been done for the endo and exopeptidases. We are attempting to pursue the three-dimensional structure using X-ray diffraction. Affinity labels are being prepared and will be used to determine amino acids at the active site.